The present invention relates to recording and reproducing a digital picture signal and, more particularly, to copy protecting television broadcast programs recorded and reproduced as a digital picture signal.
Television broadcast programs are recorded and played back by a viewer using a video tape recorder (VTR). The VTR may be an analog VTR, but analog technology cannot record a TV program with high image quality and, as a result, the reproduced analog TV broadcast program has a lower image quality than the originally broadcast TV program.
A commercially available digital VTR, on the other hand, offers high image recording quality. With the digital VTR, therefore, the reproduced TV program has virtually the same image quality as the originally broadcast TV program.
Copyright protection of video programs on video tape is available in both analog and digital VTRs. In the analog VTR, a copyright protection signal is inserted into the blanking interval of the pre-recorded analog video signal. The copyright protection signal prevents the analog VTR from copying a copyright protected analog video program from a commercially available analog video tape. The digital VTR provides a Serial Copy Management System (SCMS) to copyright protect a digital video program on a digital video tape. A form of the SCMS copyright protection system has been used to prevent copying of audio data recorded on a Digital Audio Tapes (DAT). The SCMS technique restricts copying, but is limited to copy protecting output digital signals and is ineffective if those digital signals are converted to analog form.
Problematically, the above-described copy protection techniques can be circumvented. If a digital VTR inserts a copyright protection code into the digital video data to prevent another digital VTR from copying the digital video program, the conversion of the digital video program to analog form could defeat such protection. An analog VTR does not recognize the digitally recorded copyright protection signal. By obtaining the analog video program from analog output terminals of the digital VTR, therefore, the above copyright protection schemes are circumvented. Worse, since the unauthorized copy is made from the high image quality reproduction of the digital VTR, an unauthorized high image quality copy is produced.
A technique for protecting a copyrighted program for use in a digital VTR has been described in Japanese Patent Applications Nos. 5-277633 and 6-82576. According to the proposed technique, a video signal is recorded with a copyright protection signal inserted into a line of the video signal together with data that specifies which line contains the protection signal. A parameter for coding the copyright protection signal is recorded in a data pack. However, the proposed technique does not copyright protect TV broadcast signals.